The present invention relates to a sheet for protecting a paint film which is difficult to deteriorate or discolor the paint film and thus is suitable for the surface protection of body, parts and the like of automobiles.
As a method for protecting automobiles and their parts which have been painted against the attack by various suspended matters such as dust and rainwater or other harmful matters that can damage, dull or discolor the paint film during shipping on truck or ship to overseas or other remote places, there has been heretofore known a method of applying a coating material mainly comprised of wax in a thickness of from 5 to 40 xcexcm. However, this method has some disadvantages. For example, it is difficult to form a wax coat with a uniform thickness, making it impossible to provide a uniform protection. Further, a wax coat is easily stained. Moreover, a wax coat is easily affected by acidic rainwater. Further, wax or other matters penetrate through the coated paint film to cause discoloration thereof. It takes much time and labor to apply and remove the wax coat. Further, this method requires the use of a solvent and the disposal of a waste liquid, causing environmental pollution.
On the other hand, various surface protective sheets comprising a support and a pressure-sensitive adhesive layer provided thereon have been known. A sheet comprising a support and a radiation-curing pressure-sensitive adhesive layer having a lowered glass transition point or a rubber pressure-sensitive adhesive layer made of a polyisobutylene or the like formed thereon has been proposed as a surface protective sheet for an adherend having a paint film, as disclosed in, for example, JP-A-2-199184 and JP-A-6-73352 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). This sheet can overcome the above-described problems.
However, this proposal is disadvantageous in that a detergent from window washer or the like penetrates into the paint film through wrinkle portions unavoidably developed during covering the adherend with the surface protective sheet and then remains in bubble portions unavoidably developed during covering the adherend to cause the paint film to swell and hence discolor or deteriorate, giving stains that are not easily removed. Such stains are remarkable particularly when those are attributable to wrinkle portions which have been developed in the direction of gravitational force.
As a result of extensive studies to overcome the above-described problems, it was found that the deterioration or discoloration of a paint film is attributed to the evaporation and the concentration of water from acidic water or detergent which has unavoidably penetrated into the paint film during or after adhering the protective sheet to the paint film.
In the light of the fact that the penetration of acidic rainwater or detergent is unavoidable, an object of the present invention is to provide a sheet for protecting a paint film, which does not deteriorate or discolor the paint film even if the protective sheet is adhered to protect the paint film under the condition containing acidic rainwater or detergent and thus can maintain the adhered state to the paint film over a long period of time without peeling off the protective sheet.
The sheet for protecting a paint film according to the present invention comprises a porous substrate and a pressure-sensitive adhesive layer formed on one surface of the porous substrate, wherein the sheet has an air permeability in a direction of sheet thickness of 20,000 sec/100 cc or less and a moisture permeability in a direction of sheet thickness of 2,000 g/m2xc2x724 hr or more, and also the porous substrate may have an ultraviolet transmission of 10% or less at a wavelength of 190 to 370 nm.
Even if acidic rainwater, detergent or the like penetrates into the interface between the sheet for protecting a paint film of the present invention and the paint film through wrinkle portions on the sheet, the water can evaporate away from a large area of the protective sheet due to the air permeability and moisture permeability of the porous substrate. Thus, evaporation or concentration of water is difficult to occur in local portions such as entrapped bubble portions.
As a result, even if the protective sheet is maintained to adhere to automobiles or other painted materials, the deterioration or discoloration of the paint film covered with the sheet can be prevented. Further, even if the protective sheet is adhered to painted materials under the condition containing acidic rainwater, detergent or the like, it is not necessary for the sheet to be peeled off and re-adhered. Thus, the sheet for protecting a paint film of the present invention can be applied to painted bodies having a vertical face.
Further, if the sheet of the present invention comprises a porous substrate which cuts ultraviolet rays, it is difficult to cause deterioration of substrate or adhesive layer even if the sheet is allowed to stand over an extended period of time under high ultraviolet intensity conditions such as outdoor. In other words, the sheet of the present invention can fairly maintain the initial strength and exhibits an excellent peelability. Thus, the sheet of the present invention is difficult to cause breakage of substrate or adhesive remaining and can be easily peeled off the painted material.
The sheet for protecting a paint film of the present invention comprises a porous substrate and a pressure-sensitive adhesive layer formed on one surface of the porous substrate. The sheet has an air permeability in a direction of sheet thickness of 20,000 sec/100 cc or less and a moisture permeability in a direction of sheet thickness of 2,000 g/m2xc2x724 hr or more. From the standpoint of the evaporatability of entrapped water in a large area, the air permeability of the sheet is preferably 10,000 sec/100 cc or less, and more preferably 5,000 sec/100 cc or less, and the moisture permeability of the sheet is preferably 3,000 g/m2xc2x724 hr or more, and more preferably 5,000 g/m2xc2x724 hr or more.
Another embodiment of the sheet for protecting a paint film of the present invention comprises a porous substrate and a pressure-sensitive adhesive layer formed on one surface of the porous substrate, wherein the porous substrate has an ultraviolet transmission of 10% or less at a wavelength of 190 to 370 nm. From the standpoint of prolonged maintenance of high peelability free from breakage of the sheet or adhesive remaining by preventing deterioration of the substrate or pressure-sensitive adhesive layer, the ultraviolet transmission of the porous substrate at a wavelength of from 190 to 370 nm is preferably 8% or less, more preferably 5% or less, and most preferably 1% or less.
Accordingly, the porous substrate which can be used is any appropriate porous material which at least has the air permeability and the moisture permeability fallen within the above defined range or the ultraviolet transmission fallen within the above defined range. In general, a sheet of processed fiber, such as nonwoven fabrics, woven fabrics or papers, can be used. From the standpoint of the simultaneous accomplishment of the prevention of deterioration or discoloration of the paint film and the good peelability of the sheet after accomplishment of protection, a sheet showing the air permeability and moisture permeability fallen within the above defined ranges and also the ultraviolet transmission falling within the above defined range is preferably used.
The fiber used to constitute the sheet of processed fiber can be any appropriate fiber. A fiber having excellent water resistance, etc. is preferable. Examples of such a fiber include fiber made of thermoplastic resins such as polyolefins (e.g., polyethylene, polypropylene, etc., which may be used alone or as mixtures thereof), polyesters and polyamides, regenerated or semisynthetic fibers such as rayon and cuprammonium rayon silk and cellulose acetate, natural fibers such as cotton, silk and wool, and mixtures thereof (mixed yarn).
A particularly preferred example of the porous substrate is a nonwoven fabric, particularly made of a thermoplastic resin fiber. The thickness of the porous substrate is not specifically limited. However, from the standpoints of strength, protection of a paint film and prevention of deformation of a paint film by the stress developed at the end of the sheet adhered to the paint film, the basis weight of the porous substrate is preferably 500 g/m2 or less, more preferably 5 to 300 g/m2 or less, and most preferably 10 to 200 g/m2.
The porous substrate having the air permeability and moisture permeability fallen within the above defined ranges can be obtained by controlling a porous structure such as a pore diameter or a thickness. Further, the porous substrate having the ultraviolet transmission fallen within the above defined range can be obtained such that ultraviolet light screening particles are contained and dispersed in a porous substrate such as a sheet of processed fiber in an appropriate method.
Examples of the method for dispersing the ultraviolet light screening particles in a porous substrate include a method of applying a coating solution containing ultraviolet light screening particles to the surface of fibers constituting the porous substrate to form a coating film thereon, and a method of forming a coating film on the surface of fibers and using the coated fibers to form a porous substrate.
Further examples of the method for dispersing the ultraviolet light screening particles in a porous substrate include a method of forming a plastic containing the ultraviolet light screening particles into fibers and using the fibers to form a porous substrate having the ultraviolet light screening particles dispersed therein, and a method comprising the combined use of the above methods. Accordingly, the method for dispersing the ultraviolet light screening particles in a porous substrate is not specifically limited, and any appropriate method can be used.
The coating solution used above may be a dispersion obtained by mixing a binder component comprising an appropriate resin such as acrylic resin, urethane resin or polyester resin, with the ultraviolet light screening particles in the presence of an appropriate medium such as an organic solvent or water. The coating solution may be commercially available as ZE-123 or ZR-100 (trade name, produced by Sumitomo Osaka Cement Co., Ltd.).
The application of the coating solution can be conducted by any appropriate coating method such as dipping, spraying, gravure coating or reverse-roll coating. The thickness of the coating film may appropriately be determined. In general, the thickness of the coating film is 40 xcexcm or less, preferably 20 xcexcm or less, and more preferably 0.5 to 10 xcexcm, from the standpoint of treatment efficiency or reduction in thickness.
On the other hand, the formation of the porous substrate having ultraviolet light screening particles dispersed therein can be conducted by, for example, a method of mixing the ultraviolet light screening particles with a thermoplastic resin, and then subjecting the resulting mixture to an appropriate nonwoven fabric-forming method such as melt blowing method or span bond method to form fibers and then accumulating the fibers.
The ultraviolet light screening particles which can be used are appropriate particles which reflect or absorb ultraviolet rays, such as titanium white, red oxide, zinc oxide, alumina, tin oxide or carbon black. In particular, titanium white and zinc oxide are preferable from the standpoint of effect of screening ultraviolet rays. The particle diameter of the ultraviolet light screening particles may appropriately be determined. In general, from the standpoint of the stability or prolonged maintenance of the dispersed state of the particles, the particle diameter is preferably 0.005 to 5 xcexcm, more preferably 0.01 to 1 xcexcm, and more preferably 0.02 to 0.5 xcexcm, based on an average particle diameter.
In the present invention, the porous substrate or its constituent fibers or the coating film may further comprise additives such as antioxidant or ultraviolet absorber, if required and necessary, for the purpose of preventing its deterioration. If the porous substrate or coating film is made of a thermoplastic resin, the incorporation of such an antioxidant or ultraviolet absorber is particularly effective to prevent deterioration.
The pressure-sensitive adhesive layer may be formed using an appropriate pressure-sensitive adhesive such as rubber pressure-sensitive adhesives or acrylic pressure-sensitive adhesives. In particular, the preferred rubber pressure-sensitive adhesive is a rubber polymer free of or having a small content of aliphatically unsaturated bond from the standpoint of prolonged stability of properties.
Examples of the rubber polymer include polyisobutylene, butyl rubber, A-B-A type block polymer such as styrene-ethylene.butylene copolymer-styrene (SEBS), styrene-ethylene.epropylene copolymer-styrene (SEPS), styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS), hydrogenated product thereof, and ethylene-vinyl acetate copolymer.
The pressure-sensitive adhesive can be prepared using one or more base polymers, preferably two or more base polymers each having different molecular weight distribution. If the base polymer is an A-B-A type block polymer, those each having different molecular weight distribution or styrene content may be used in combination. Alternatively, such an A-B-A type block polymer may be used in combination with an A-B type diblock polymer such as styrene-ethylene.butylene copolymer (SEB), styrene-ethylene.propylene copolymer (SEP), styrene-butadiene (SB) or styrene-isoprene (SI).
In preparing the pressure-sensitive adhesive, an appropriate tackifier such as terpene resin (e.g., xcex1-pinene polymer, xcex2-pinene polymer, diterpene polymer, xcex1-pinene.phenol copolymer), hydrocarbon resin (e.g., aliphatic resin, aromatic resin, aliphatic-aromatic copolymer resin), rosin, cumarone-indene resin, (alkyl)phenol resin or xylene resin may be blended with the base polymer, if required and necessary, for the purpose of controlling the adhesive properties or like.
Further, the adhesive properties or other properties can also be controlled by the incorporation of an appropriate softening agent depending on the base polymer, e.g., low molecular weight polyisobutylene or polybutene for polyisobutylene or paraffin oil for A-B-A type block polymer, if required and necessary. In addition, an appropriate additive such as filler, pigment, antiaging agent or stabilizer may be incorporated in the pressure-sensitive adhesive, if required and necessary.
The pressure-sensitive adhesive layer may be applied to all over the surface of the substrate. However, the pressure-sensitive adhesive layer is preferably in the form of a porous layer from the standpoint of the prevention of deterioration or discoloration of the paint film due to the accomplishment of the desired air permeability and moisture permeability of the sheet for protecting a paint film. The formation of the porous adhesive layer can be conducted by any appropriate method such as a method of subjecting a pressure-sensitive adhesive to melt blowing or curtain spray to form fibers and then accumulating the fibers in the form of, for example, a nonwoven fabric or a method of partly applying a pressure-sensitive adhesive to the substrate in a dot or stripe pattern.
The pressure-sensitive adhesive layer may also be a porous layer formed by subjecting a pressure-sensitive adhesive layer comprising a continuous film to a perforation treatment. In this embodiment, a liquid which has penetrated into the holes in the pressure-sensitive adhesive layer is contacted with the adjacent porous substrate, and diffuses in the porous substrate. The perforation treatment may extend to the porous substrate.
In particular, a porous pressure-sensitive adhesive layer obtained by a melt blowing method which comprises melting a pressure-sensitive adhesive, and blowing the molten adhesive onto the substrate in the form of fiber through a high pressure air is preferable because deviation in adhesive force, air permeability and moisture permeability is small, thereby attaining the desired adhesive force and water evaporatability at the same time. The pressure-sensitive adhesive to be used in the melt blowing method is preferably a hot melt type pressure-sensitive adhesive which can be extrusion coated. In particular, a pressure-sensitive adhesive comprising the A-B-A type block polymer as a base polymer is preferably used.
The formation of the sheet for protecting a paint film can be conducted according to the conventional method for the formation of an adhesive sheet, such as a method of applying a solvent solution or heat-fused solution of a pressure-sensitive adhesive to the porous substrate or a method of transferring a pressure-sensitive adhesive layer formed on a separator onto the porous substrate. The thickness of the pressure-sensitive adhesive layer thus formed may appropriately be determined. The thickness is generally 3 to 100 xcexcm, preferably 7 to 70 xcexcm, and more preferably 10 to 50 xcexcm.
The sheet for protecting a paint film which is preferable from the standpoint of adhesion workability on adherends such as automobiles and water evaporatability has an apparent density of 0.8 g/cm3 or less, preferably 0.7 g/cm3 or less, and more preferably 0.6 g/cm3 or less. If desired and necessary, the pressure-sensitive adhesive layer thus formed may be protected by temporarily adhering a separator or the like thereto until it is put into practical use.
The sheet for protecting a paint film of the present invention is preferably used for the surface protection or paint film protection of a body or their parts such as bumper of automobiles, coated with a paint film such as polyester.melamine paint, alkyd.emelamine paint, acryl.melamine paint, acryl.urethane paint or acryl.polyacid curing agent paint, or other coated products such as coated steel plate, against the collision of fine particles or attack by chemicals.
In particular, the sheet for protecting a paint film of the present invention can advantageously be used where acidic rainwater or chemicals such as acidic liquid tends to easily penetrate into the protective sheet because the adhesion-covering work of the protective sheet to the adherend is conducted outdoor or in the factory, etc., or where acidic rainwater or detergent from window washer tends to easily penetrate into the interface between the sheet and the paint film during the outdoor storage, etc.